Printing devices, such as liquid jet printers, may feed liquid ink through a substrate to a firing port. While the liquid ink is fed through the substrate, such as through a channel that extends through the substrate, the liquid ink will come into contact with the channel walls. In an example wherein the substrate is manufactured of silicon and the liquid ink is a pigmented ink including charged dispersants, the liquid ink may etch the channel wall of the substrate such that silicon leaches into the pigmented ink. The presence of silicon in the ink may cause a blockage or partial blockage of the firing port. It may be desirable to reduce such blockage or partial blockage of the firing port to improve the print quality of the printing device.